System hangs during BIOS phase

This sounds like a power problem, either in the power supply or in capacitors on the motherboard.  Your cold boots are not always successful, but your warm boots are.  This is usually due to failing capacitors somewhere, which have a chance to store up charge initially, even though it isn't enough to boot, but the reset can boot because there is a charge from the previous power-on.

If it hangs at the BIOS it's definitively a hardware issue.

It's really hard to determine based on the fact that it's the BIOS and nothing responds. My suggestion use a trial an error approach to the issue.

First you can use unplug the computer and press and hold the power button for at least 10 seconds, it could just be some energy left on the circuits. Sometimes it happens.

If you plugged new hardware lately, try unpluggin it and testing. Also try to run some diagnostics when you are able to boot up properly. Try swapping memory from other servers if you have one available. If the problem remains then you will need a more massive approach, which will take time but you should hit the issue there.

Remove everything removable, leave the computer just with the keyboard, mouse and monitor. From there start plugging and making sure everything is reseated properly. HDD, Removable Drives, Video Card, NIC, etc.

That way you should encounter the problem. Try flashing BIOS too if new updates are available.

Hope this is helpful.

It's hard to determine what is causing the problem.

I would suspect that it's a hardware issue since a bootup that hangs at the bios hasn't even touched the OS yet.

I would strip the machine down to bare bones and try booting up.  If it boots then start adding components back in one at a time until it hangs again and there's your culprit.

If being stripped down and it still hangs that will be a bit trickier.

Make sure you remove all hard drives and leave only one stick of memory in.

Also remove any cards that are not absolutely necessary.

On a smaller scale I had a laptop that acted the same way.  Turned out that it was a bad HD causing the problem.  I swapped out the HD and the machine booted.  The problem followed the HD to another laptop.

What performance issue has caused the sudden change?   That might be a clue.

The performance issue:

Yesterday users reported severely impaired performance of network database applications.  Transactions that normally take less than a second were taking minutes to complete.

The administrator rebooted the server.  At that reboot the first observation of hang during the BIOS occurred.

After successful restart of the server the network applications performed normally.

Could be PSU or memory.

Make sure your backups are working properly.  Saving data would be my biggest concern.  You can always replace hardware...data needs to be recreated.

My first steps on this problem have been to image the system partition and confirm all backups are current.

I agree with you, ScottCha, about protecting the data.

At exactly what point in the boot process does it hang?  e.g. while identifying drives or loading ESCD information.

i would calculate the power neede for this system, or replace the power supply :
http://extreme.outervision.com/psucalculator.jsp      

The system hangs during the Dell splash screen a progress bar prior to the text phase of the boot.  When it hangs the screen contains the text in the upper right corner of the screen stating "F2 - Setup...".
The progress bar stops at about 25% indicated progress.  It does not get to the next screen in which details
about the BIOS used and info about drives is displayed.

The PSU calculator recommended indicates less than 250 w required.

try resetting the bios to default values, or reset it with the onboard jumper; if none exists, remove the battery and power cord for 5 minutes

Also see if you can change BIOS setting to verbose mode on boot rather than splash screen.  Helps to know exactly what's happening.

Test the voltages on the power supply. Do you have redundant power supplies?

The machine has a single power supply.  

I will have my first opportunity to revisit the problem server today ( 11/8 ) and will use the suggestions presented above.

ADDED OBSERVATION:  since my last post with data about the problem a spontaneous shutdown and restart occurred on this PC.  During the restart the problem presented in my original post occurred.  On manaul restart the system booted up fine.

I will post results from work done today by tomorrow.

Thanks for your help with this.

crm

I inspected the motherboard and power supply for evidence of capacitor leakage or damage to other components and found no clear signs of problems.  

Since the problem PC is a server the downtime was very limited and voltage testing and component removal and testing did not fit in the time available.

A key change I have made is to remove an external hard drive that used a USB connection to the system.  We have had problems with the backups to that drive and suspected a problem with the backup software.  After moving the external drive to another computer the backup problems appear to be resolved.  Also performance problems on the PC that had been hanging on reboot disappeared.

Although it is not technically conclusive I suspect the USB system may be involved in the abnormal behavior of the PC and will, in the interest of closing this long open issue, accept the response from acesover2000.

Thank you all for your insight, suggestions and helpfulness with this issue.

crm

I had that EXACT same problem.. slow backups (sometimes never finishing) and slow performance.  I ultimately needed the USB connections though, so I purchased a second USB (PCI-X) controller for my HP ML370 and now it works like a charm (plus I have USB 2.0 now when I only had 1.1 before)  The chipset and BIOS upgrades did not address my problem.

Good luck.  Thanks for the points